Stream Discharge Response to Climate Change and Land Use Change in Tamor Basin, Nepal

Abstract

Climate change and land use change are two major issues that need to be addressed for sustainable land and water resource management. These are major factors influencing discharge in monsoon dominated basin. This study aims to quantitatively assess the impact of climate change and land use change on future discharge of the Tamor basin in Nepal. Result from the study indicated maximum temperature will reach to 40.63°C in 2030s, 40.63°C in 2060s and 45.95°C in
2090s which was 35°C in baseline period (1976-2005). Annual average precipitation was projected to change by 17.64% under RCP 4.5 and by 39.88% under RCP 8.5 till the end of the century as projected by HadGEM2. Since the basin is monsoon dominated, annual discharge was projected to increase by 12.25% under RCP 4.5 and by 32.67% under RCP 8.5 above baseline average till the end of the century. Result using HadGEM2 also shows that peak flows that used to occur in August in baseline period will shift to July except in 2030s under RCP 4.5. However, CSIRO-Mk3.6.0 projects decrease in annual precipitation and hence also discharge at the end of the century. Result from both Global Climate Models show that average monthly discharge due to climate change will change positively as well as negatively for both scenarios. Due to combined impact of land use change and climate change, annual discharge was projected to change by 16.53%, 21.28% and -4.39% under RCP 4.5 and by 38.29%, 45.64% and 13.06% under RCP 8.5 till the end of the century for conversion of forest into agricultural land, conversion of forest into barren land and conversion of barren land into forest respectively. Average annual discharge increased the most in case of conversion of forest into barren land and decreased or increased the least in case of conversion of barren land into forest. Unlike annual, seasonal response to combined impact was different. In monsoon and pre monsoon, discharge increased or decreased the least in case of conversion of forest into agricultural land and barren land while increased the least or decreased in case of conversion of barren land into forest. However, in post monsoon and winter, discharge decreased the least or increased the most in case of conversion of barren land into forest but discharge decreased the most or increased the least in case of conversion of forest into agricultural land and barren land.